Background: Irish-descended people in Britain experience elevated mortality and morbidity, compared with white British people, persisting across generations. Reasons are unknown. Objectives: 1. To determine the prevalence of: childhood and adulthood psychological morbidity, poorer self-rated health, alcohol misuse and tobacco use, in second generation Irish people relative to the rest of the sample, in a nationally representative cohort. 2. Assess life-course experiences of adversity in second generation Irish people relative to the rest of the samples. 3. Assess how far life-course adversity mediates the association between second generation Irish ethnicity and health outcomes. Methods: Data from the National Child Development Survey (NCDS) and The 1970 British Birth Cohort (BCS70), in which 17,000 babies born in 1958 and 1970, respectively, followed up until adulthood, was used. 6% were of second generation Irish descent. Results: Second generation Irish people grew up in marked material disadvantage. By mid-life, Irish people had reached parity with the rest of the cohort on most adversity indicators. Irish children were more likely than the rest of the cohort to experience psychological morbidity at 7, 11 and 16 (NCDS) OR 16 (BCS70). This diminished after adjustment for parental health and material hardship. By mid-life, second generation Irish cohort members were more likely to screen positive for common mental disorders (OR: 1.27 (95% CI: 0.96-1.69)), poorer self-rated health (OR: 1.25 (95% CI: 0.98-1.60)), binge alcohol use (OR 1.26 (95% CI: 1.00-1.58)) and tobacco use (OR: 1.29 (95% CI: 1.05-1.58)). Associations between Irish ethnicity and all health outcomes were either fully or partially attenuated after adjustment for childhood adversity. Conclusions: Second generation Irish people in Britain experience adverse mental and physical health over their life-course. This may be due to growing up in circumstances of marked childhood adversity.